The present invention in the first place relates to a method for treating seed with a fluid, in particular water, involving the use of a fluid-containing gas.
In intensive agriculture it is important to supply high-quality seeds that germinate well, rapidly and uniformly. To improve the seed quality in these respects, seed which in the dry state shows hardly any metabolic activity and therefore is resting, is activated (xe2x80x9cprimingxe2x80x9d) by the seed being treated, for example, with water. As a result, the resting stage is interrupted and germination is stimulated. The treatment causes the seed to take up water (imbibition), as a result of which germination processes, not observable from the outside, commence in the germ.
The treatment with water does however entail a major risk that the seeds will actually germinate (i.e. that the root tip penetrates the pericarp). What should be aimed for, however, is to interrupt the water treatment just prior to the moment of germination, so that germination will not occur. After the treatment the seeds can be sown or can be dried (dehydrated). What has been found is that the pretreated, dehydrated seeds exhibit a high degree of germination synchronicity when they are sown and, moreover, keep well in this dry state.
The treatment with water does, however, have various problems which even today have not yet been resolved.
A method is known in the prior art which involves seeds being treated with steam in a rotating drum (U.S. Pat. No. 5,119,589). The steam condenses on the inside of the drum, with which the seeds keep coming into contact owing to the rotary movement of the drum. The seeds absorb this moisture and are removed from the wall by means of a scraper. This method has the drawback that the seeds are subjected to considerable physical stress, entailing a high risk that the seed will be damaged and will not germinate.
It is an object of the present invention to overcome the abovementioned drawbacks, the invention to this end being characterized in that seed is brought into contact with a gas having a controlled fluid content and the seed is kept in contact with the gas over a defined period whilst direct contact between the seed and the fluid in liquid form is substantially precluded.
The method of the present invention provides an excellent pretreatment of seed, without the latter coming into contact with fluid in liquid form and without the seeds having to be exposed to mechanical stress, as the fluid in question can be directly taken up by the seeds from the gas phase. It has also been found that with the aid of the method according to the present invention very precise pretreatment of the seeds can be ensured. Moreover, it has been found that a treatment according to the present invention leads to high-quality pretreated seed.
In this context reference is made to Allen et al., (Hort. Science, Volume 27 (4), pp. 364-366), who describe a method for pretreating seed with water by incubating the seed in an aqueous polyethylene glycol solution having a defined osmotic potential. This method, also referred to as xe2x80x9cosmoprimingxe2x80x9d, is generally known, but is expensive, given the large quantities of polyethylene glycol which are needed, and requires complicated treatment steps, during which large quantities of polluting polyethylene glycol have to be discharged in some way. Moreover, the uptake of oxygen by the seed is hindered by the viscous polyethylene glycol. Alternatively, the seeds can be subjected to osmotic treatment on a solid support, as described in U.S. Pat. No. 4,912,874. With this method, large quantities of polluting wastes are formed and there is a risk of the seed being damaged.
Preferably, the gas phase is substantially stationary and the fluid transport through the gas phase towards the seed takes place substantially via diffusion. With a stationary gas phase it has been found that the seed takes up the fluid very uniformly and slowly, diffusion processes playing a crucial part. The slower water uptake has advantages over the more rapid water uptake taking place in the case of osmopriming and water/steam treatment.
In particular, the fluid comprises water, in an amount of 99% or more. Whilst the method, in principle, is suitable for the pretreatment of the seeds with any liquid, the pretreatment generally takes place with water. This water can also contain supplementary substances such as minerals, hormones, pesticides and/or stimulants. Such substances can, however, also be added to the gas phase, if desired. For decontamination purposes use can be made, for example, of water containing chlorine bleach, for example in a concentration of 0.4 w/w%.
It should be clear that where the application refers to xe2x80x9cfluid content of the gas phasexe2x80x9d this can be read, in the case of water as the fluid used, as xe2x80x9crelative humidityxe2x80x9d. If the gas phase is formed by air, the abovementioned term is comparable with xe2x80x9crelative air humidityxe2x80x9d.
The optimum relative humidity for priming depends on the seed to be primed. It has been found that very good priming is achieved if the relative air humidity is 98% or more. In a preferred embodiment of the present invention, the relative humidity is 98% or more, more preferably 99% or more. Optimum priming is generally achieved if the humidity is maintained just below the saturation point in the gas, without saturation of the gas with the fluid occurring. Thus the moisture content is as high as possible, as a result of which priming of the seed can take place very rapidly and effectively. A fluid-saturated gas is undesirable, as there is then the risk that the fluid will condense on the seed, which can be deleterious as already described above.
Advantageously, the temperature of the gas is between 2 and 40xc2x0 C., preferably between 8 and 30xc2x0 C. In the latter temperature range good priming takes place, although higher or lower temperatures are possible. At higher temperatures, however, problems may occur, since not all types of seed may be resistant to such high temperatures.
Below 5xc2x0 C., moisture will indeed penetrate the seeds, but the resting stage will not or virtually not be disturbed, and priming generally takes place to an insufficient degree.
Preferably, the temperature of the seed at the beginning of the treatment is between 8 and 35xc2x0 C., as this temperature range corresponds to the temperatures to which the seeds or plants are generally exposed in nature.
Preferably, the temperature of the seed at the beginning of the treatment is equal to or higher than that of the gas. This prevents, at the beginning of the treatment, liquid or water from condensing on the outside of the seeds, the seeds thereby coming into contact with the liquid, with all the deleterious consequences already described above. Condensation on the seeds also results in a lower germination synchronicity being achieved.
Advantageously, the seed is treated over a period of 1-14 days. A longer treatment may lead to unwanted germination, whilst a shorter treatment may lead to inadequate synchronicity, as a result of a large number of seeds still being in the germination resting stage because they have not taken up enough water. The optimum duration of the treatment may differ between types of seed.
It has been found, surprisingly, that if the seed prior to the abovementioned fluid treatment is incubated in an environment which is saturated with said fluid, it is possible for optimal and well-synchronized accelerated priming to be achieved. The fact is that it has been found that the seeds which, in the dry state, have an osmotic pressure of from xe2x88x92400 to xe2x88x92100 MPa, first take up a considerable amount of water before the seeds become physiologically active and priming proper starts. This physiologically active phase sets in when the seed has taken up so much water that its osmotic pressure is greater than xe2x88x9210 MPa. xe2x80x9cGreater than xe2x88x928 MPaxe2x80x9d refers to an osmotic pressure whose value is above xe2x88x928 MPa. In principle this therefore means that a higher value amounts to a lower water uptake capacity. The said phase usually commences when the osmotic pressure of the seed is between xe2x88x921.2 and xe2x88x928 MPa. It is noted that the measurement of the osmotic pressure of seed can take place by general methods known in the prior art. Reference is made in this context to L. W. Woodstock, Journal of Seed Technology Vol. 12, no. 1 (1988).
During the physiologically active phase, the seeds are sensitive to being damaged. At the first water uptake (i.e. until the osmotic pressure has decreased to about xe2x88x928 MPa), the seeds can in principle take up water in any manner chosen at will, for example in an environment saturated with the said fluid, for example by the seeds being sprayed, the seeds being immersed in water, or by the seeds being incubated on filter paper saturated with water. Only when the said osmotic pressure of greater than xe2x88x928 MPa has been reached is it important for the seeds to be brought into contact with water in such a way that the water is taken up more slowly (the actual priming process).
Thus the method, according to another aspect of the invention, relates to treating seed with water, which at least comprises the steps of:
incubation of the seed in a water-saturated environment until the osmotic pressure of the seed is greater than xe2x88x9210 MPa, preferably between xe2x88x921.2 MPa and xe2x88x928 MPa,
subsequent incubation of the seed under conditions of delayed water uptake.
This delayed water uptake can take place, in principle, in a manner known from the prior art, for example by the abovementioned osmopriming or steam treatment. Preferably, the seed, until the desired osmotic pressure of from xe2x88x921.2 MPa to xe2x88x928 MPa has been reached, is incubated in the fluid-saturated environment. For most seeds, a period of from 4 to 24 hours proved sufficient for the said osmotic pressure to be reached. It should be clear that the incubation time may vary depending on the type of seed. This incubation time and other conditions can be optimized empirically by those skilled in the art.
Preferably, the seeds are thus first incubated for 4-24 hours in a water-saturated environment and then in a chamber, substantially whilst precluding direct contact between seed and fluid in liquid form, at a relative air humidity of at least 98%. As already set out above, the seeds, once they have taken up sufficient water and the osmotic pressure of the seeds is from xe2x88x921.2 MPa to xe2x88x928 MPa, are sensitive to being damaged. As a result of the remaining water uptake being made to occur at a relative air humidity of at least 98%, without direct contact between seed and fluid in liquid form, substantially no damage will be caused to the seeds, while optimal synchronized priming takes place. During the priming process, the osmotic pressure of the seeds is brought to a value of between approximately xe2x88x921.2 to xe2x88x921.5 MPa and/or is maintained over a suitable period. It should be understood that if the seed, by direct water contact, has already acquired an osmotic pressure of between xe2x88x921.2 and xe2x88x921.5 MPa, no water has to be taken up by the seeds during the conditions of delayed water uptake, but that the osmotic pressure of the seeds is maintained at the said value.
The invention further provides seed obtainable by the method according to the invention and also a plant which is obtained from seed that has been pretreated by means of the method according to the present invention.
The invention further relates to an apparatus, designed particularly for implementing the method according to the invention, at least comprising a substantially closed chamber having supply and discharge means for a fluid, means being present for forming a transfer surface between the fluid and the gas in the chamber, and temperature control means being present for controlling a temperature difference between the fluid and the gas contained in the chamber. By means of this apparatus, an open fluid stream can be formed within a gas space. If the temperature of the air is chosen to be higher than that of the fluid stream, condensation of the fluid vapour from the gas phase onto the fluid stream can take place in a controlled manner, i.e. the relative air humidity of the gas phase can thereby be maintained below the saturation point in a controlled manner.
Conversely it is possible, by means of an apparatus of this type, for evaporation of the fluid from the open fluid stream into the gas phase to be effected in a controlled manner by the temperature of the air being kept below that of the fluid stream. This embodiment, however, has proved less relevant for use in the apparatus for priming seed.
It has been found that in the case of water as the fluid and air as the gas, a temperature difference of 0.1xc2x0 C. involves a change in relative air humidity of 0.5%. Thus the relative air humidity can be maintained at 99.5% by choosing the temperature of the air to be 0.1xc2x0 C. higher than that of the flowing fluid. If this temperature difference is 0.3xc2x0 C., the relative air humidity will thus be about 98.5%. For a temperature difference of this type of 2xc2x0 C., the relative air humidity is 90%.
An apparatus of this type thus allows very high air humidity below the saturation point to be maintained in the chamber in a controlled manner, without incurring the risk of the gas becoming saturated with the fluid. For example, it is possible to set a sustained stable high relative air humidity to an accuracy of 0.1-0.2%, for example 98%xc2x10.2%, which are the optimum conditions for treating seed according to the present invention.
It is noted that the invention is also suitable for fluids other than water. Alternatively, for example, an oxygen-enriched air mixture can be used instead of air.
The temperature control means for controlling the temperature difference between the fluid and the gas in the chamber can advantageously comprise heating and/or cooling means in the wall of the chamber for heating or cooling, respectively, the gas contained in the chamber. Furthermore, it is also possible to control the temperature of the water feed.
The temperature of the wall of the chamber can thus be set to a value that differs from the temperature of the water, the gas contained in the chamber adopting the temperature of the wall of the chamber.
In order for a large and effective transfer surface to be obtained, the means for forming the transfer surface preferably comprise means for forming a flowing fluid layer in the chamber.
It has been found, surprisingly, that with the use of water as the fluid and air as the gas phase, a very high relative air humidity (above 98%) can be maintained in a controlled manner; the temperature difference between the temperature of the water and the temperature of the wall is small in this case (less than 0.6xc2x0 C.), provided that the temperature of the wall and therefore of the gas contained in the chamber is higher than that of the water.
Advantageously, the means for controlling the temperature of the wall and/or the means for controlling the temperature of the fluid can be set such that a temperature difference between the fluid in the chamber and the wall of the chamber of 0.1xc2x0 C. or less can be achieved. It is technically possible to control and maintain such a temperature difference between the water feed and the wall of the chamber, and this can be effected with the aid of means known from the prior art.
Given a temperature difference of this type of 0.1xc2x0 C. it is possible for a relative air humidity in the chamber to be set accurately to 99.5%xc2x10.2%. If required it is possible, likewise by adjusting the temperature difference, to set a correspondingly altered relative air humidity to the same accuracy, for example to 98.0%xc2x10.2%.
In a following preferred embodiment the apparatus according to the invention comprises moistening means for bringing the seed directly into contact with the liquid. As already set out hereinabove, it is advantageous for the seeds first to be caused to take up water by direct water contact such as spraying, until the osmotic pressure of the seeds is from about xe2x88x921.2 MPa to xe2x88x928 MPa. By means of the moistening means, which can, for example, take the form of sprayers and can be incorporated in the wall of the apparatus, it is possible for the seeds to be sprayed directly with water which can then be taken up by the seeds. The seeds can be sprayed over a desired period, after which the air humidity can be set to 98% or more in the above-described manner, in order to complete the priming process.
The invention further provides a method for operating the apparatus according to the invention, which involves the seed to be treated with fluid being brought into the closed chamber, water being caused to flow through the chamber in such a way that the water can be taken up in the gas phase, and the temperature of the wall being set to a temperature which is above that of the water, the temperature difference between the water and the wall being at most 0.6xc2x0 C., preferably at most 0.4xc2x0 C. By virtue of this temperature difference, a high relative air humidity of more than 98% can be obtained within the chamber, at which humidity level priming of the seed contained in the chamber, can take place. Preferably, the temperature difference is at most 0.2xc2x0 C. With such a low temperature difference, a relative air humidity of 99%xc2x10.2% can be achieved.
After the correct amount of water has been taken up, the seeds can either be sown directly or alternatively be dried again, in order for the seeds to be sown at a later time.
The invention further relates to a method for treating seed as described hereinabove, which involves increasing the temperature of the wall after treatment of the seed is complete, in order to set a fluid content below 98% in the gas phase of the chamber, these measures being taken in such a way that the fluid is abstracted from the seeds. Drying of the seeds takes place as soon as the relative air humidity drops below 98%. Obviously, if required, the air humidity can be set to any value below 98% by the said temperatures being controlled. As already set out hereinabove, a relative air humidity of 90% can be maintained by setting the temperature difference to 2xc2x0 C. As a result of the seeds being kept in the apparatus for a defined period at a relative air humidity below 98%, drying (xe2x80x9cdehydrationxe2x80x9d) can take place.
The invention will be described in more detail with reference to the accompanying drawing, in which the single figure shows a cross-section of an embodiment of the apparatus according to the present invention in simplified form.
An apparatus 1 comprises a chamber 2 with a gas, which is delimited by a wall 3 and a cover 15. Incorporated in the wall 3 are spiral cooling and heating elements, respectively (not shown). The chamber holds a quantity of seed 5 in nets 6, which are suspended in the chamber 2. The number 10 indicates a hollow tube placed in the centre in the apparatus 1. Through the interior of tube 10, water is supplied via a feed line 8 and is distributed over the outer surface of the tube 10. As a result, a large transfer surface is obtained between the water and the gas space 2. The water is collected and removed via a discharge 9. Positioned at the location of the fluid inlet is a temperature sensor 11 for measuring the temperature of the fluid feed. A hygrometer 12 measures the air humidity of gas space 2. The temperature of the chamber 2 is measured by a temperature sensor 13. A temperature sensor 14 measures the temperature of the wall. Not shown are means connecting one or more measuring instruments to a control unit, which can be linked to control means (likewise not shown) for the cooling and heating elements 4 of wall 3 and for temperature adjustment means for the water to be fed in. The control unit can also comprise a data input.
During operation, water, whose flow direction is indicated in the figure by means of arrows, is introduced into the apparatus 1 via the line 8 and is distributed over the outer surface of the tube 10. The temperature of the wall is higher than that of the water feed, so that during the transport of the water across the tube 10 the uptake of water vapour from the gas phase into the water is effected. This results in a lowering of the relative humidity with respect to the saturation point in the chamber 2. The water coming from the outer surface of the hollow tube 10 is collected by discharge 9 and is removed.
Depending on the desired relative air humidity in chamber 2, the temperature difference between the water feed and the temperature of wall 3 can be set with the aid of the above-described control unit and control means, which are linked to the measuring instruments 11, 12, 13 and 14. The seeds contained in the chamber can be introduced into the gas space 2 and be removed by cover 15 being opened. As a result of the seeds not coming into direct contact with the fluid, no condensation will take place on the seeds, as long as the temperature of the seeds, when they are introduced into the apparatus, is not below that of the air in chamber 2.